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Message-ID: <472631FE.9070003@google.com>
Date: Mon, 29 Oct 2007 12:18:22 -0700
From: Mike Waychison <mikew@google.com>
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To: Zach Brown <zab@zabbo.net>
CC: Chris Mason <chris.mason@oracle.com>, Anton Altaparmakov <aia21@cam.ac.uk>,
       linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 0/6][RFC] Cleanup FIBMAP
References: <20071026233732.568575496@crlf.corp.google.com>	<E579083F-FED3-4990-8E24-275ED38E9E3B@cam.ac.uk> <20071029101001.4378a7cf@think.oraclecorp.com> <47260AB1.9000003@zabbo.net>
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Zach Brown wrote:
>>> And another of my pet peeves with ->bmap is that it uses 0 to mean  
>>> "sparse" which causes a conflict on NTFS at least as block zero is  
>>> part of the $Boot system file so it is a real, valid block...  NTFS  
>>> uses -1 to denote sparse blocks internally.
>> Reiserfs and Btrfs also use 0 to mean packed.  It would be nice if there
>> was a way to indicate your-data-is-here-but-isn't-alone.  But that's
>> more of a feature for the FIEMAP stuff.
> 
> And maybe we can step back and see what the callers of FIBMAP are doing
> with the results they're getting.
> 
> One use is to discover the order in which to read file data that will
> result in efficient IO.
> 
> If we had an interface specifically for this use case then perhaps a
> sparse block would be better reported as the position of the inode
> relative to other data blocks.  Maybe the inode block number in ext* land.
> 

Can you clarify what you mean above with an example?  I don't really follow.

Thanks,

Mike Waychison


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